Theoretical study of the mechanism for the gas‐phase pyrolysis kinetics of 2‐methylbenzyl chloride

The study of the kinetics and mechanism of dehydrochlorination reaction of 2‐methyl benzyl chloride in the gas phase was carried out by means of electronic structure calculations using ab initio Móller‐Plesset MP2/6‐31G(d,p), and Density Functional Theory (DFT) methods: B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p)], PBE/6‐31G(d,p), PBE/6‐31++G(d,p). Investigated reaction pathways comprise: Mechanism I, a concerted reaction through a six‐centered cyclic transition state (TS) geometry; Mechanism II, a 1,3‐chlorine shift followed by beta‐elimination and Mechanism III, a single‐step elimination with simultaneous HCl and benzocyclobutene formation through a bicyclic type of TS. Calculated parameters ruled out Mechanism III and suggest the elimination reaction may occur by either unimolecular Mechanism I or Mechanism II. However, the TS of the former is 20 kJ/mole more stable than the TS of the latter. Consequently, the Mechanism I seem to be more probable to occur. The rate‐determining process is the breaking of C‐Cl bond. The involvement of π‐electrons of the aromatic system was demonstrated by NBO charges and bond order calculations. The reaction is moderately polar in nature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 537–546, 2011     

Study of the thermal decomposition of a sepiolite by mid- and near-infrared spectroscopies

Near-infrared (NIR) and mid-infrared (MIR) spectroscopies were used to characterize the hydroxyl groups present in a sepiolite and its calcination products at 250, 500 and 800 °C. Calcining the sepiolite at 250 °C was found to result in its dehydration through the loss of coordination water. Raising the calcination temperature to 500 °C caused the sepiolite structure to fold and hydroxyl groups in octahedral layers to be removed. Finally, calcination at 800 °C resulted in a phase change leading to enstatite, as confirmed by XRD spectroscopy.     

Ion-pair evaporation from ionic liquid clusters

A differential mobility analyzer (DMA) is used in atmospheric pressure N₂ to select a narrow range of electrical mobilities from a complex mix of cluster ions of composition (CA)_n(C⁺)_z. The clusters are introduced into the N₂ gas by electrospraying concentrated (～20 mM) acetonitrile solutions of ionic liquids (molten salts) of composition CA (C⁺ = cation, A^? = anion). Mass analysis of these mobility-selected ions reveals the occurrence of individual neutral ion-pair evaporation events from the smallest singly charged clusters: (CA)_nC⁺→(CA)_{n? 1}C⁺+CA. Although bulk ionic liquids are effectively involatile at room temperature, up to six sequential evaporation events are observed. Because this requires far more internal energy than available in the original clusters, substantial heating (～10 eV) must take place in the ion guides leading to the mass analyzer. The observed increase in IL evaporation rate with decreasing size is drastic, in qualitative agreement with the exponential vapor pressure dependence predicted by Kelvin’s formula. A single evaporation event is barely detectable at n = 13, while two or more are prominent for n ≤ 9. Magic number clusters (CA)₄C⁺ with singularly low volatilities are found in three of the four ionic liquids studied. Like their recently reported liquid phase prenucleation cluster analogs, these magic number clusters could play a key role as gas-phase nucleation seeds. All the singularly involatile clusters seen are cations, which may help understand commonly observed sign effects in ion-induced nucleation. No other charge-sign asymmetry is seen on cluster evaporation.     

Aerosol size standards in the nanometer size range II. Narrow size distributions of polystyrene 3-11 nm in diameter

A technique for generating charged aerosols of polystyrene (pSty) with narrow size distributions has been developed. It is based on electrospraying commercial narrow mass standards of pSty dissolved in l-methyl-2-pyrrolidone (NMP) seeded with the newly synthesized salt dimethyl ammonium formate. This salt imparts a much larger electrical conductivity than previously known NMP electrolytes, leading to higher quality sprays with greatly reduced attachment of impurities. Controlling the solute concentration enables forming polystyrene particles containing from one up to more than ten single polystyrene molecules, whereby 4 mass standards with molecular weights from 9200 up to 96,000 g/mol yield particles covering densely the diameter range from 3 to 11 nm. Combined mobility and mass measurement with a differential mobility analyzer and a mass spectrometer in tandem are carried out with a pSty sample 9200 amu in molecular weight. They fix directly the mass versus mobility relation near 9200 amu, and indirectly for the other standards and their clusters. The apparent particle density resulting from mobility versus mass data agrees with the bulk density of the polymer, indicating that the particles are dense and spherical. Although these standards have been studied only in gaseous suspension, their injection in liquids such as water where pSty is insoluble should keep them spherical.     

Stress regularity in quasi-static perfect plasticity with a pressure dependent yield criterion

This work is devoted to establishing a regularity result for the stress tensor in quasi-static planar isotropic linearly elastic – perfectly plastic materials obeying a Drucker–Prager or Mohr–Coulomb yield criterion. Under suitable assumptions on the data, it is proved that the stress tensor has a spatial gradient that is locally squared integrable. As a corollary, the usual measure theoretical flow rule is expressed in a strong form using the quasi-continuous representative of the stress.     

Development and validation method for determination of fluoxetine and its main metabolite norfluoxetine by nonaqueous capillary electrophoresis in human urine

A simple, rapid and sensitive procedure using nonaqueous capillary electrophoresis (NACE) to measure fluoxetine and its main metabolite norfluoxetine has been developed and validated. Optimum separation of fluoxetine and norfluoxetine, by measuring at 230 nm, was obtained on a 60 cm × 75 μm capillary using a nonaqueous solution system of 7:3 methanol-acetonitrile containing 15 mM ammonium acetate, capillary temperature and voltage 25 °C and 25 kV, respectively and hydrodynamic injection. Paroxetine was used as internal standard. Good results were obtained for different aspects including stability of the solutions, linearity, and precision. Detection limits of 10 μg L⁻¹ were obtained for fluoxetine and its metabolite. This method has been used to determine fluoxetine and it main metabolite at clinically relevant levels in human urine. Before NACE determination, the samples were purified and enriched by means of extraction-preconcentration step with a preconditioned C₁₈ cartridge and eluting the compounds with methanol.     

The Lattice Solid Model to Simulate the Physics of Rocks and Earthquakes: Incorporation of Friction

The particle-based lattice solid model developed to study the physics of rocks and the nonlinear dynamics of earthquakes is refined by incorporating intrinsic friction between particles. The model provides a means for studying the causes of seismic wave attenuation, as well as frictional heat generation, fault zone evolution, and localisation phenomena. A modified velocity–Verlat scheme that allows friction to be precisely modelled is developed. This is a difficult computational problem given that a discontinuity must be accurately simulated by the numerical approach (i.e., the transition from static to dynamical frictional behaviour). This is achieved using a half time step integration scheme. At each half time step, a nonlinear system is solved to compute the static frictional forces and states of touching particle-pairs. Improved efficiency is achieved by adaptively adjusting the time step increment, depending on the particle velocities in the system. The total energy is calculated and verified to remain constant to a high precision during simulations. Numerical experiments show that the model can be applied to the study of earthquake dynamics, the stick–slip instability, heat generation, and fault zone evolution. Such experiments may lead to a conclusive resolution of the heat flow paradox and improved understanding of earthquake precursory phenomena and dynamics.